The present invention relates to an application device for applying a coating liquid such as a photographic photosensitive liquid, a magnetic liquid or a surface-protective liquid to a moving flexible carrier made of a plastic film, paper, a metal sheet or the like and hereinafter referred to as a web.
Conventional application devices for applying a liquid to a web include those of the roll type, the bead type, the slide coating type, and the extrusion type. In the application device to which the present invention relates, the liquid is discharged under appropriate pressure from the slit of an application head of the device, as in the conventional application device of the extrusion type. Since the width of the conventional application device of the extrusion type corresponds to that of the web, which is about 0.5 m to 3.0 m, the device has the problem that it is difficult to make the thickness of the applied liquid on the web uniform along the width thereof In particular, when a magnetic liquid of high viscosity is applied to a web with the conventional application device of the extrusion type, the liquid is discharged under prescribed pressure from the slit of the application head of the device while the head is urged against the moving web to apply the liquid thereto In this device, it is very difficult to make the distribution of the pressure of the magnetic liquid uniform along the length of the slit. Therefore, the thickness of the liquid applied to the web is not uniform along the width of the web.
In order to solve this problem, various application devices in which the width of the slit of an application head for applying a liquid to a web can be adjusted to enhance the uniformity of the thickness of the applied liquid on the web have been proposed, as disclosed, for instance, in Japanese Unexamined Published Patent Applications Nos. 291117/86 and 2610225/86.
In the application device disclosed in application No. 291117/86, the liquid discharge portion of the application head 20 is provided with a lip 21, a recess 22, and a plurality of screws 24, as shown in FIG. 8. The lip can be moved forward & and aft by manipulating the screws. However, it is very difficult and hardly possible to manipulate the screws 24 during the application of the liquid to the web. Since the liquid discharge portion of the application head 20 is provided with the lip 21, the recess 22, and the screws 24, the head is difficult to manufacture and the maintenance thereof is cumbersome. The freedom of design of the head is also quite limited.
In the application device disclosed in Application No. 261022/86, a force is applied to the lip 22 of the liquid discharge portion of the application head 20 by screws 24, as shown in FIG. 9. Also, the head 20 is provided with heaters 25 capable of heating the shanks of the screws 24 to expand them. Thus, the screws 24 do not need to be manually manipulated. However, the construction of the application head 20 is again complex, its maintenance difficult, and the freedom of design limited. Moreover, the cost of this application head is high.